The long range goal of this research is to develop a mechanical ventilator that has the potential to reduce morbidity and mortality in critically ill pediatric patients. Our novel approach controls the pressure in the patient's airway using a unique pinch-valve, jet nozzle and venturi system. The conventional approach for infants uses a valve placed at the end of several feet of exhalation tubing. Our new valve will direct gas flow through a nozzle jetting the gas into the patient's airway to control airway pressure during inhalation. During exhalation, the valve directs a combination of gas flows to the venturi and nozzle to control tracheal pressure. The response time of the new design is so rapid that airway pressures during inhalation and exhalation can be prescribed very accurately, much in the fashion that a musical synthesizer can be programmed to give specific sounds. The potential advantages of this innovative design are that one ventilator can be used: 1) for patients ranging in size from the very low birth weight preterm infant to the 30 kg child; 2) in either the pressure-limited time-cycled mode or a volume control mode; 3) at both conventional rates and high frequency rates (ranging from 1 to 660 breaths/min); 4) to reduce CO2 in the anatomic dead space so that smaller tidal volumes may be used; 5) to control tracheal pressure during spontaneous breathing and, thus, to decrease the work of breathing by eliminating the endotracheal tube resistance to gas flow; because of its rapid response time capabilities; 7) to give a visual display of tracheal airway pressure and gas flow. Completion of the research plan will result in a valve-nozzle-venturi system for mechanical ventilation which will simplify and improve as delivery to infants and children. Six prototype ventilators will be constructed for multi-centered clinical studies using an investigational device exemption (IDE) protocol approved by the FDA.